Test-write method, information recording method, and information recording apparatus

ABSTRACT

A test-write method for accurately and quickly determining recording conditions, and an apparatus suitable therefor. In a 2T-based strategy, recording pulse conditions are determined by separately test-writing an even-number length mark and an odd-number length mark, and then the relative positions of the even-number length mark and the odd-number length mark at the recording pulse start time are adjusted.

CLAIM OF PRIORITY

The present application claims priority from U.S. patent applicationSer. No. 10/931,040, filed Sep. 1, 2004, which claims priority fromJapanese application JP 2004-222742 filed on Jul. 30, 2004, the contentof which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a test-write method, and an informationrecording method and apparatus for recording information by injectingenergy into a recording medium to form a mark different from anunrecorded portion.

2. Background Art

Test writes are performed in order to record information on an opticaldisc with high accuracy. A test write refers to the operation ofdetermining optimal recording parameters depending on the immediateambient temperature and the characteristics of the laser mounted on adrive so that a recording mark with better quality can be formed. Inoptical discs such as DVD-RW, DVD+RW, and BD-RE, a material with aso-called eutectic composition is used in the recording film. In thecurrently commercially available recording apparatuses, when performinga test write in the aforementioned optical discs, the recordingconditions written in the optical disc beforehand are read out and thenthe laser power is adjusted. The recording conditions include laserpower set values, such as a recording power level (Pw) which is of highlaser power, an erasing power level (Pe) which is of intermediate power,and a bias power level (Pb). The recording conditions further includevarious pulse widths of pulses forming a multi-pulse waveform, includinga first pulse, a plurality of subsequent intermediate pulses, and a lastpulse.

In an actual test write, a technique is used whereby, based on theserecording conditions, the ratio of Pw and Pe that are written in theoptical disc in advance is fixed, and the optimum recording conditionsare determined using the laser power as a parameter. This method iscalled an Optimum Power Control (OPC). In relatively slow-speedrecordings, such as BD 1× speed or DVD-RW 2.4× speed, good recordingquality could be obtained by performing a test write by varying only thelaser power with a constant Pw/Pe ratio.

Research and development of high-speed recording and reproductiontechnology for the aforementioned optical discs are progressing. Forexample, in Optical Data Storage 2003, Proceedings of SPIE Vol. 5069(2003), p. 130 (Non-Patent Document 1), there is described a recordingtechnique involving a recording speed of 216 Mbps, which corresponds toBD 6× speed. As the recording speed increases, there has also been anadvance in the study of recording waveforms suitable for higher speeds,or the so-called 2T-based strategy. The 2T-based strategy involves arecording waveform such that the number of recording pulses is the samefor an adjacent pair of even-number length mark and odd-number lengthmark. For example, as shown in FIG. 2, in a case where a minimum marklength is 2T, a single pulse is generated for a 2T mark and a 3T mark,and two pulses consisting of a first pulse and a last pulse aregenerated for a 4T mark and a 5T mark. For a 6T mark and a 7T mark, atotal of three pulses, namely a first pulse, one intermediate pulse, anda last pulse, are generated.

An example of the 2T-based strategy is disclosed in JP PatentPublication (Kokai) No. 9-134525 A (1997) (corresponding to U.S. Pat.No. 5,732,062; Patent Document 1). The example relates to a multi-pulserecording method using a first pulse, a plurality of subsequentintermediate pulses, and a last pulse, wherein, when recording either aneven-number length mark or an odd-number length mark relative to arecording channel clock period, the pulse width of the first pulse andthat of the last pulse are made substantially equal to the recordingchannel clock period.

In another example, JP Patent Publication (Kokai) No. 11-175976 A (1999)(corresponding to U.S. Pat. No. 6,256,277; Patent Document 2) disclosesa technique using a recording waveform such that a minimum pulse widthin the multiple pulses is set to be larger than one half the windowmargin. By so doing, the publication reads, a sufficient cooling timefor the recording medium can be ensured and the frequency component inthe laser drive current can be reduced, so that marks can be formed withsufficient accuracy even at high transfer speeds.

JP Patent Publication (Kokai) No. 2003-30833 A (Patent Document 3)discloses a recording technique whereby not only is the period ofintermediate pulse strings made longer than the recording channel clockperiod, as in JP Patent Publication (Kokai) No. 11-175976 A (1999), butalso the edge position of the first pulse and that of the last pulse arevaried depending on a preceding space or a subsequent space. Thepublication states that this method can minimize the edge shift due tothermal interference in a track direction, which poses a problem in ahigh-density and high-transfer rate recording, and allows ahigh-accuracy recording control to be realized.

JP Patent Publication (Kokai) No. 2001-331936 A (corresponding to U.S.2001/053115 A1; Patent Document 4) discloses that the reference clock isdisplaced for an even-number code sequence and an odd-number codesequence, and that, for even-number and odd-number recording pulsewaveforms, the duty ratio of the first pulse and the last pulse ischanged between even numbers and odd numbers.

The recording mark-shape controlling effect of the 2T-based strategy inhigh-transfer rate recording is described in Optical Data Storage 2000,Proceedings of SPIE Vol. 4090 (2000), p. 135 (Non-Patent Document 2),for example.

-   [Patent Document 1] JP Patent Publication (Kokai) No. 9-134525 A    (1997)-   [Patent Document 2] JP Patent Publication (Kokai) No. 11-175976 A    (1999)-   [Patent Document 3] JP Patent Publication (Kokai) No. 2003-30833 A-   [Patent Document 4] JP Patent Publication (Kokai) No. 2001-331936 A-   [Non-Patent Publication 1] Optical Data Storage 2003, Proceedings of    SPIE Vol. 5069 (2003), p. 130-   [Non-Patent Publication 2] Optical Data Storage 2000, Proceedings of    SPIE Vol. 4090 (2000), p. 135

SUMMARY OF THE INVENTION

In the above-described test write method according to the conventionalart, or the OPC method, best-quality recording conditions are determinedby optimizing the laser power with Pw/Pe kept constant. However, theinventors' analysis has shown that if recording speeds of BD 4× orDVD±RW 8× or higher are to be achieved, it is difficult to obtain a goodmark quality with the OPC method, in which the laser power with a fixedPw/Pe is used as the parameter. This is due to the following reasons. Incases of low-speed recording, such as BD 1× and DVD±RW 2.4×, there issufficient time between the irradiation of the aforementioned firstpulse and the irradiation of the next pulse (intermediate or last pulse)that the recording film can be sufficiently cooled before the next pulseirradiation. However, in cases of high-speed recording, the time betweenthe irradiation of the first pulse and the irradiation of the last pulseis reduced such that the cooling speed of the recording film would berelatively insufficient, leading to the problem that the leading edgeformed by the first pulse cannot be sufficiently cooled. If the nextpulse is irradiated when the leading edge is not sufficiently cooled,crystallization occurs in the leading edge portion, which leads to edgefluctuation or edge shift. This is equivalent to a deterioration of markquality. Thus, there is the problem that the recording performance isadversely affected by an increase in speed.

Moreover, as the recording speed increases, the individual variation inthe characteristics of the laser mounted in commercially availabledrives cannot be disregarded. For example, the recording channel clockperiod T at BD 4× speed is approximately 3.8 ns, and the laser waveformmust be controlled below 1 ns. However, since the rise and fall time ofcurrent lasers are on the order of 1 to 2 ns, the waveform control onthe order of 1 ns is close to physical limits, where the individualdifferences in the rise and fall of the laser come to significantlyaffect the shape of a recording mark. Further, the problems ofindividual differences in apparatuses that could be absorbed by themedium in the case of low-speed recording, such as the difference inemission waveforms between different drives due to drive-to-drivevariations in the spot size, come to the fore in high-speed recording.

The invention has the following features.

(1) Mark lengths in a recording code sequence are classified intorecording patterns according to the remainder when, with regard to marksof lengths that are n times the window margin, where n is a naturalnumber, n is divided by an integer constant of 2 or larger. Theresultant recording patterns are recorded and then reproduced, and basedon the result of reproduction, an optimum recording pulse waveform isset. In this way, the pulse adjusting amount can be made constant foreach of the recording patterns classified according to the remainder, sothat an optimum pulse adapted for high speed can be efficientlyobtained.

For example, in the case of the 2T-based strategy, an even-number lengthrecording pattern composed of recording marks with a lengthcorresponding to an even-number multiple of the reference clock period,and an odd-number length recording pattern composed of recording markswith a length corresponding to an odd-number multiple are respectivelyrecorded and then reproduced. Based on the result of the reproduction,an even-number length optimum recording pulse waveform and an odd-numberlength optimum recording pulse waveform are set. In other words, in thecase where the temporal length of a single recording mark is nT (where Tis the reference clock period, n is a natural number of 2 or larger),when forming a recording waveform for test write using a recording laserbeam consisting of a number L of pulses, the recording patterns consistof (A) an even-number length recording pattern formed by marks nT=2LT,namely recording marks with a length corresponding to an even-numbermultiple of the reference clock period, and (B) an odd-number lengthrecording pattern formed by marks nT=(2L+1)T, namely recording markswith a length corresponding to an odd-number multiple. The even-numberlength recording pattern (A) and the odd-number length recording pattern(B) are recorded and then reproduced. Based on the result of thereproduction, an optimum recording pulse waveform is set on the basis ofthe thus determined even-number length recording pulse waveform and theodd-number length recording pulse waveform.

In the case of a 3T-based strategy, where nT=3LT, a recording pattern(A) formed by marks with nT=3LT, a recording pattern (B) formed by markswith nT=(3L−2)T, and a recording pattern (C) formed by marks withnT=(3L−1)T are recorded. Then, an optimum recording pulse waveform isdetermined based on the resultant three sets of recording pulsewaveforms.

In the case of a 4T-based strategy, where nT=3LT, a recording pattern(A) formed by marks with nT=4LT, a recording pattern (B) formed by markswith nT=(4L−2)T, a recording pattern (C) formed by marks withnT=(4L−1)T, and a recording pattern (D) formed by marks with nT=(4L+1)Tare recorded. Then, an optimum recording pulse waveform is determinedbased on the resultant four sets of recording pulse waveforms.

(2) With regard to the setting of the optimum pulse waveform, an optimumrecording pulse waveform is set by adjusting the relative positionalrelationship between the first-pulse irradiation start positions of therecording pulse waveforms classified by the remainder. In this way, anoptimum recording waveform can be obtained by a simple configuration.(3) It is possible to absorb the variations in the rise and fall oflaser in the individual apparatuses or spot shape differences in eachapparatus by making Pw and Pe independently variable rather than usingthe laser power with constant Pw/Pe as the parameter for test write andby making the pulse width and the pulse start position variable. Byemploying such parameters, an emission waveform can be set by takinginto consideration the cooling time of the medium, so that the edgefluctuation and edge shift can be minimized. These parameters may all bechanged during a test write. Alternatively, some parameters may be fixedand others may be changed so as to obtain an optimum waveform.

In the case of the 2T-based strategy, it is effective to carry out atest write separately for the even-number length mark and the odd-numberlength mark.

These methods are effective not only with optical discs of the type thathas a single recording film layer but also with optical discs with aplurality of recording film layers. For example, in the case of anoptical disc with two recording layers, there is the problem that therecording margin in each recording layer becomes narrower than that inthe case of a disc with a single recording layer. However, in accordancewith the invention, the recording margin can be enlarged by individuallysetting the recording power Pw and the erasing power Pe and making thepulse width variable, in addition to only controlling the laser power.

These measures are particularly effective when performing a test writein rewritable media that employ an eutectic recording film, such asDVD-RW, DVD+RW, and BD-RE.

By performing such a test write, it may in some cases take more timethan by the conventional art. However, in media for which the term“burn” is used to refer to recording, such as DVD±RW and BD-RE, the timeit takes for a test write is 2 to 3 seconds, while it takes far longertime (such as 10 minutes) to “burn” (record). Thus, even if the time fora test write increased by five times, there would be not much change inthe duration of time in which the user must be kept waiting, so that theusability of the optical disc does not become any worse and nodisadvantages are caused to the user.

In accordance with the invention, the accuracy of a test write can beincreased, so that an optical disc with a higher recording quality thatis adapted for high speed can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process flowchart of a test-write method according to anembodiment of the invention.

FIG. 2 shows an example of a recording pulse waveform used in theinvention.

FIG. 3 shows an example of a recording pulse waveform used in theinvention.

FIG. 4 shows a process flowchart of a test-write method according to anembodiment of the invention.

FIG. 5 shows an example of a recording pulse waveform used in theinvention.

FIG. 6 shows an example of a test-write region used in the case where atest-write recording pattern for even-number length marks and that forodd-number length marks are used.

FIG. 7 shows an example of the relationship between a first pulse startposition, an intermediate position, and jitter.

FIG. 8 shows an example of an apparatus used in the invention.

FIG. 9 shows an example of a test-write pattern used in the invention.

FIG. 10 shows an example of a recording pulse waveform used in theinvention.

FIG. 11 shows a process flowchart of a test-write method according to anembodiment of the invention.

FIG. 12 shows an example of a recording pulse waveform used in theinvention.

FIG. 13 shows a process flowchart of a test-write method according to anembodiment of the invention.

FIG. 14 shows an example of an apparatus used in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described by referring to thedrawings.

Embodiment 1

First, the recording method used in the present embodiment will bedescribed. When writing data on an optical disc, a mark-edge recordingmethod employing multiple pulses is used, whereby the data is written inthe disc in terms of length information about marks and spaces. Themodulation method employed was such that the length of a mark and aspace was a combination of integer values 3T to 14T. FIG. 3 shows anexample of the recording waveform used in the present invention. In thepresent embodiment, the 2T-based strategy was employed. A 3T mark isformed by a single pulse, and a 4T mark and a 5T mark are formed by twopulses, namely a first pulse and a last pulse. A 6T mark and a 7T markare formed by a total of three pulses, namely a first pulse, a lastpulse, and a single intermediate pulse. An 8T mark and a 9T mark areformed by a total of four recording pulses, namely a first pulse, a lastpulse, and two intermediate pulses. Thereafter, the number ofintermediate pulses increases as the mark length increases. When arecording mark is nT (where T is a reference clock period, and n is anatural number of 2 or larger), even-number length marks such as 4T and6T marks can be expressed by nT=2LT, while odd-number length marks suchas 3T and 5T marks can be expressed by nT=(2L+1)T, where L is a naturalnumber and indicates the number of recording pulses.

The disc employed was a rewritable DVD (a red light-source adaptedphase-change disc) capable of 12× speed recording, with a linearvelocity of approximately 41.9 m/s. The clock period T in FIG. 3 isabout 3.2 ns.

The invention is described with reference to FIG. 1 showing a flowchartof the operation of the test write method according to the presentembodiment. In a first step (S101), the recording conditions recorded onthe disc, such as a recommended recording power and pulse width, wereread, obtaining a recording power (Pw) of 130 mW, an erasing power (Pe)of 6 mW, and a bias power (Pb) of 0.5 mW. In a second step (S102), laserpower conditions were set in these vicinities. In a third step (S103), atest write was carried out on the disc. The laser power conditions weresuch that the value of Pb was fixed, Pw/Pe was not a fixed value, and Pwwas varied between 116 mW and 144 mW in increments of 2 mW, and Pe wasvaried between 5.5 mW and 6.5 mW in increments of 0.5 mW. As a result ofthe test write in the third step (S103), a minimum jitter of 6.2% wasobtained when Pw was 134 mW and Pe was 6 mW, in a fourth step (S104).Preferably, the test-write recording pattern used in the third step forobtaining the optimum recording power should not be a so-called randomsignal in which all of the mark lengths and space lengths are variouslycombined. In the case of a high-speed recording, if a random signal isrecorded without optimizing the recording waveform such as the recordingpulse width, the jitter would not decrease in some cases even near thesupposedly optimum recording power. This is due to the fact that therecording is carried out using an inappropriate recording waveform and,as a result, the problem occurs that a laser power that should have beenan optimum power cannot be selected. For this reason, the test-writerecording pattern used in the third step should preferably be a simplerecording pattern that would not produce mark-to-mark thermalinterference, such as one consisting of a repetition of the same marksand spaces, or one using several kinds of marks and a long space.

Using the optimum recording power selected in the fourth step, arecording was carried out in a fifth and a sixth step (S105 and S106) inorder to determine the optimum conditions regarding the recording pulsewidth of the recording mark and the start position of the recordingpulse. In this case, it is important to carry out the recording using atest-write pattern consisting only of even-number length marks and atest-write recording pattern consisting only of odd-number length marks,as shown in FIG. 1. In the present embodiment, in the even-number lengthmark test-write pattern, six kinds of even-number length marks, namely4T, 6T, 8T, 10T, 12T, and 14T, and 12 kinds of lengths of spaces, namely3T to 14T, are randomly disposed. Similarly, in the odd-number lengthmark test-write pattern, six kinds of odd-number length marks 3T, 5T,7T, 9T, 11T, and 13T, and 12 kinds of lengths of spaces 3T to 14T aredisposed in a random manner. In the present example, the space lengthsin these recording patterns include mixtures of even-number lengths andodd-number lengths. With regard to the space length, there is no need toprovide such limitations as providing only even-number length spaces inan even-number length test-write pattern.

In the 2T-based strategy, the number of recording pulses in aneven-number length mark and that in an odd-number length mark in anadjoining pair are the same. For example, as shown in FIG. 3, a 4T markand a 5T mark are each made up of two recording pulses, and a 6T markand a 7T mark are made up of three recording pulses. What is unique hereis that the Pb-level pulse width (W1) after the irradiation of the firstpulse of the 4T mark is substantially the same as that (W1) of the 6Tmark. Similarly, the Pb-level pulse width (W2) after the irradiation ofthe first pulse of the 5T mark is substantially the same as that (W2) ofthe 7T mark. The front edge position of a recording mark formed by afirst pulse is influenced by the start position of the recording pulsethat comes after the first pulse. For example, as the recording pulsethat comes after a first pulse is located increasingly away from thefirst pulse, there would be less region that is recrystallized after themelting of the recording film. As a result, there would be not muchshrinkage of the front edge position, so that the front edge positionwould be fixed at a position closer to the front edge of the moltenregion. Conversely, as the recording pulse that comes after the firstpulse is located closer to the first pulse, there would be more regionthat is recrystallized after the melting of the recording film. As aresult, there would be much shrinkage in the front edge position, suchthat the front edge position would be fixed further behind the moltenregion.

The influence of the irradiation of the recording pulse that comes afterthe first pulse (an intermediate pulse or a last pulse) on the frontedge position is thought to be substantially the same between the 4Tmark and 6T mark, and between the 5T mark and 7T mark. As shown in FIG.3 (not shown in FIG. 2), an 8T mark has a front edge position that issimilar to that in a 4T and a 6T mark. By utilizing a test-writerecording pattern consisting only of marks with such similar thermalcharacteristics, the increase in jitter due to the fluctuation of theedge position caused by multiple kinds of recording pulse shapes can bemade less visible, so that an optimum recording pulse width can bedetermined accurately and efficiently.

Using the recording waveform of each recording mark that is set with thepulse width and position of a recording pulse that satisfy the optimumconditions determined in the seventh and eight steps (S107 and S108), atest write was carried out in a ninth step (S109). Specifically, usingthe relative positions of the first pulse start position of theeven-number length mark and that of the odd-number length markdetermined in steps S107 and S108 as a parameter, ΔT shown in FIG. 3 wasdetermined. As a result of the test write in the ninth step (S109), anoptimum ΔT of 0.07 Tw and an optimum jitter of 6.4% were obtained in atenth step (S110).

While the intermediate pulse width in the present embodiment was thesame for both the even-number length mark and the odd-number lengthmark, yet better recording conditions may be obtained by setting thewidth of the intermediate pulse or its duty variously individually.

In the present embodiment, with regard to the 3T mark formed by a singlepulse, the recording pulse conditions including the first pulse positionwere independently set. This is due to the fact that the 3T mark is madeup of a single pulse and therefore the process of determining the frontedge position is different from that of the other marks made up of aplurality of recording pulses. In the present embodiment, the recordingpulse conditions for the 3T mark were determined in step S109 of a testwrite, as well as determining ΔT in the tenth step (S110).

While in the present embodiment the number of recording pulses of nT=2LTand nT=(2L+1)T are equal such that the 4T mark and the 5T mark have thesame number of recording pulses, the same effects of the invention canbe obtained when the recording pulses for nT=2LT and nT=(2L−1)T areequal such that the number of pulses is the same for 5T and 6T.

Further, in the present embodiment, a test write was carried out byusing the start position of the first pulse of each recording mark as anindividual parameter. Specifically, the start position and pulse widthof the first pulse, the start position and pulse width of theintermediate pulse sequence, and the start position and pulse width ofthe last pulse of each mark were determined. As a result, as shown inFIG. 3, the start position of the first pulse relative to the clock wasthe same between even-number length marks of lengths of 4T mark or more,and so was the start position of the first pulse between odd-numberlength marks of lengths of 5T mark or more. Thus, the optimum startposition of the first pulse in some cases turn out to be the samebetween even-number length marks and between odd-number length marks.Therefore, in a test write on an actual production-model drive, bysetting the start position of the first pulse to be the same beforehandin each test-write recording pattern used in steps S105 and S106, thetime required for the test write can be reduced and the area that isrequired for the test write can be reduced.

While in the present embodiment the jitter was used as the factor forthe evaluation of reproduction characteristics, the same effects of theinvention can be obtained even when the type of the evaluation factor ischanged. For example, PRML may be used for the evaluation ofreproduction performance.

Furthermore, while in the present embodiment the recording power Pw andthe erasing power Pe were variable, it is also possible to determine theoptimum recording conditions by making the pulse width variable whileusing the recommended recording power recorded on the disc as a fixedvalue. In this method of test write, the number of parameters is reducedas the laser power is a fixed value, so that the time required for thetest write can be reduced and the area used for the test write can alsobe reduced.

An actual recording of user data is carried out using the recordingwaveform obtained as a result of the test write.

Embodiment 2

In Embodiment 1, the test-write recording pattern was divided into aneven-number length mark expressed by nT=2LT and an odd-number lengthmark expressed by nT=(2L+1)T which were then individually recorded inorder to obtain an optimum recording waveform. Namely, in Embodiment 1,as shown in FIG. 6, if one track is used for the test write fordetermining the optimum recording waveform for an even-number lengthmark, another one track is necessary for the test write for determiningthe optimum recording waveform for an odd-number length mark.

In the present embodiment, there are provided in a single test-writerecording pattern a recording pattern region consisting only ofeven-number length marks and a recording pattern region consisting onlyof odd-number length marks (see FIG. 9, referenced by numeral 1). Thereproduction characteristics of each pattern region are then measured inorder to improve the efficiency of test write. Specifically, a recordingpattern consisting of even-number length marks and a recording patternconsisting of odd-number length marks are continuously formed.

The disc used was a phase-change disc adapted for a blue light sourcecapable of 6× speed recording. The linear velocity was about 31.7 m/s.FIG. 4 shows a flowchart of the operation of the test-write methodaccording to the present embodiment. In a first step (S201), therecording conditions such as the recommended power were read from thedisc, obtaining a recording power (Pw) of 18 mW, an erasing power (Pe)of 3.4 mW, and a bias power (Pb) of 0.25 mW. In a second step (S202),the laser power conditions were set in these vicinities, and then a testwrite was carried out on the disc in a third step (S203). The laserpower conditions were such that Pw was varied between 16 mW and 20 mW inincrements of 0.2 mW, and Pe was varied between 3.1 mW and 3.7 mW inincrements of 0.2 mW, while fixing the value of Pb. As a result of thetest write in the third step (S203), a minimum jitter of 4.5% wasobtained when Pw was 18.2 mW and Pe was 3.2 mW, in a fourth step (S204).

Using the optimum recording power selected in the fourth step (S204), arecording was carried out in a fifth step (S205) in order to determinethe optimum conditions for the recording pulse width of a recording markand the start position of a recording pulse. In this case, there wereprovided in a single test-write recording pattern a recording patternregion consisting only of even-number length marks (nT=2LT) and arecording pattern region consisting only of odd-number length marks(nT=(2L+1)T). The reproduction signals from these recording patternregions were individually measured and evaluated to determine theoptimum recording pulse conditions for the even-number length marks andodd-number length marks individually. The pulse width was varied inincrements of 1/16T. As a result, a pulse width of 0.88T was obtainedfor the first pulse width of an even-number length mark, against a setvalue 0.81T. For the first pulse width of an odd-number length mark, apulse width of 0.94T was obtained against a set value of 0.88T. Whilethe first pulse widths have been described here, the last pulse widthand the fall pulse width of a cooling level following the irradiation ofthe last pulse were also optimized.

Using the recording waveform of each recording mark that has been setwith the pulse width and position of the recording pulse that satisfiesthe optimum conditions determined in the sixth and seventh steps (S206and S207), a test write was carried out in an eight step (S208).Specifically, using as parameters the relative positions of the startposition of the first pulse of the even-number length mark and that ofthe odd-number length mark as determined in S206 and S207, ΔT shown inFIG. 2 was determined. As a result of the test write in the eighth step(S208), an optimum ΔT of 0.1T and an optimum jitter of 5.0% wereobtained in a ninth step (S209).

With regard to the mark formed by a single pulse, such as the 2T markand the 3T mark, the recording pulse conditions including the firstpulse position were independently set, as in Embodiment 1. This is dueto the fact that since the 2T and 3T marks are made up of a singlepulse, the process of determination of the front edge position isdifferent from that of the other marks made up of a plurality ofrecording pulses. In the present embodiment, the recording pulseconditions for the 2T and 3T marks were obtained in step S208 of testwrite, as well as determining ΔT in the ninth step (S209).

Finally, the optimum recording power determined in step S204 was finelyadjusted in S210. While in step S204 the minimum jitter was obtainedwhen Pw was 18.2 mW and Pe was 3.2 mW, in step 210, the minimum jitterwas obtained when Pw was 18.5 mW. Pe was the same at 3.2 mW. Thus, therecording power is finely adjusted after it is determined and therecording pulse conditions are set using the recording power. In thisway, more appropriate recording conditions can be determined.

In an actual recording, a recording waveform determined based on thetest write is used.

Embodiment 3

In Embodiment 2, a recording pattern region consisting only ofeven-number length marks and a recording pattern region consisting onlyof odd-number length marks were provided in a single test-writerecording pattern. In the present embodiment, a so-called random signalis used in the test-write recording pattern, the random signalconsisting of a combination of all of the mark lengths and spacelengths. Upon reproduction, the random signal is read separately for theeven-number lengths and odd-number lengths and the optimum recordingconditions are determined for the even-number length marks and theodd-number length marks. In this method, the reproductioncharacteristics are measured from a single recording pattern separatelyfor the even-number lengths and odd-number lengths, so that there is noneed to prepare a special test-write recording pattern. Therefore, asmaller number of changes are required to be made in the existingsystem. Further, as compared with the test-write method employingrecording patterns separately for even and odd numbers, the time andregion required for a test write can be reduced.

The disc used in the present embodiment was the same as that ofEmbodiment 2. The linear velocity was also the same at about 31.7 m/s.FIG. 11 shows a flowchart of the operation of the test write methodaccording to the present embodiment. The first (S301) through the fourth(S304) steps are the same as those of Embodiment 2 (S201 to S204) andare therefore not described herein for simplicity.

Using the optimum recording power (Pw 18.2 mW, Pe 3.2 mW) selected inthe fourth step (S304), a recording was carried out in order todetermine the optimum conditions regarding the recording pulse width ofa recording mark and the start position of a recording pulse. In thepresent embodiment, a random signal was used as the test-write recordingpattern. In sixth and seventh steps (S306 and S307), the reproductionsignal of even-number length marks and that of odd-number length marksthat were randomly arranged were simultaneously measured. The signalswere then evaluated separately for even-number lengths and odd-numberlengths. In eighth and ninths steps (S308 and S309), the optimumrecording pulse conditions for the even-number length marks andodd-number length marks were separately determined.

Using the recording waveform of each recording mark that has been setwith the pulse width and position of the recording pulse that satisfiesthe optimum conditions determined in the eighth and ninth steps, a testwrite was carried out in a tenth step (S310). Specifically, using asparameters the relative positions of the start position of the firstpulse of the even-number length mark and that of the odd-number lengthmark as determined in S308 and S309, ΔT shown in FIG. 2 was determined.As a result of the test write in the tenth step (S310), an optimum ΔT of0.1T and an optimum jitter of 5.1% were obtained in an eleventh step(S311), which were comparable to those of Embodiment 2.

The marks formed by a single pulse, such as the 2T mark and the 3T mark,were handled in the same manner as in Embodiment 2. As a result of fineadjustment of the optimum recording power (S312), Pw of 18.5 mW and Peof 3.2 mW, which are the same as those of Embodiment 2, were obtained.

The above-described method is effective not just with optical discs witha single recording film layer but particularly as a test write methodfor optical discs of the type that has a plurality of recording filmlayers. In the case of a BD-RE 4× speed-adapted optical disc with tworecording layers, the recording margin in each recording layer isnarrowed by 2 to 5 points as compared with the recording margin of asingle-layer 4× speed BD-RE disc. However, by setting the recordingpower Pw and the erasing power Pe individually or making the pulse widthvariable in accordance with the invention, in addition to the control ofthe laser power, the recording margin can be expanded to the same degreeas that of the single-layer BD.

Embodiment 4

In Embodiment 2, because of the use of the 2T-based strategy, thetest-write recording pattern was divided into even-number length marksand odd-number length marks. In the present embodiment, a 3T-basedstrategy is employed. The 3T-based strategy involves a recording systemin which the number of recording pulses expressed by nT=3LT, nT=(3L−2)T,and nT=(3L−1)T is the same. For example, 4T to 6T marks are made up oftwo recording pulses, and 7T to 9T marks are made up of three recordingpulses. FIG. 5 shows the 3T-based strategy.

In the present embodiment, using the disc used in Embodiment 2 and atester, three kinds of test-write recording patterns were recorded whichconsisted of mark lengths expressed by multiples of 3, mark lengthsexpressed by multiples of 3 from which 1 was subtracted, and marklengths expressed by multiples of 3 from which 2 was subtracted.Specifically, a test-write pattern for an nT=3LT mark consisted of twokinds of marks, namely 6T and 9T marks, and 12 kinds of lengths ofspaces, namely 3T to 14T, that were randomly arranged. Similarly, atest-write pattern for an nT=(3L−1)T mark consisted of two kinds ofmarks, namely 5T and 8T marks, and 12 kinds of lengths of spaces 3T to14T, that were randomly arranged. A test-write pattern for an nT=(3L−2)Tmark consisted of two kinds of marks 4T and 7T and 12 kinds lengths ofspaces 3T to 14T that were randomly arranged.

Each pulse width and pulse start position were then determined as inEmbodiments 1 and 2. Thereafter, ΔT1 which is the difference in pulsestart position between the nT=(3L−1)T mark and the nT=(3L−2)T mark shownin FIG. 5 (such as the distance between 4T and 5T, or between 7T and 8T)was determined as a parameter. Further, ΔT2 which is the difference inpulse start position between the nT=(3L−1)T mark and the nT=3LT mark(such as the distance between 5T and 6T, or between 8T and 9T), namelythe relative first pulse positions of the nT=(3L−1)T mark and the nT=3LTmark, was determined as a parameter. As a result, 0.07T was obtained forboth ΔT1 and ΔT2.

Embodiment 5

In the present embodiment, an example of a 4T-based strategy adapted foreven higher speeds is described that uses a phase-change disc capable of8× speed recording and adapted for a blue light source. The 4T-basedstrategy involves a system in which the number of recording pulsesmaking up each of four adjoining mark lengths is the same. For example,the same number of recording pulses are used for the marks expressed bynT=4LT, nT=(4L−2)T, nT=(4L−1)T, and nT=(4L+1)T.

An example of such a test-write recording pattern is shown in FIG. 10.5T to 8T marks are made up of two recording pulses, 9T to 12T marks aremade up of three recording pulses, and 13T and 14T marks are made up offour recording pulses. Using this 4T-based strategy, a test-writerecording was carried out. In the present embodiment, as in Embodiment 3a random signal was used in which all of the mark and space lengths werecombined in the test-write recording pattern. Upon reproduction, therandom signal was read in four groups of patterns, and then the optimumrecording conditions were determined for each of the four groups.Specifically, the aforementioned four groups of patterns are a group of5, 9, and 13T marks, a group of 6, 10, and 14T marks, a group of 7 and11T marks, and a group of 8 and 12T marks. The individual pulse widthand pulse start position were then determined as in the above-describedembodiments, and then the relative positions of the first pulse startpositions of the four groups were adjusted. In the present embodiment,the recording pulses for the 3T mark and the 4T mark were independentlyset.

A test write was carried out in the same manner as in theabove-described embodiments, and there were obtained parameters ΔT1 thatis the difference in the pulse start position between the nT=(4L−2)Tmark and the nT=(4L−1)T mark, ΔT2 that is the difference in the pulsestart position between the nT=(4L−1)T mark and the nT=4LT mark, and ΔT3that is the difference in the pulse start position between the nT=4LTmark and the nT=(4L+1)T mark, as shown in FIG. 10. As a result, ΔT1 andΔT3 were 0.05T and ΔT2 was 0.061. With regard to the first pulse width,only the marks expressed by nT=(4L+1)T, namely the group of 5, 9, and13T marks, had a different value from the set value, or shorter by1/16T.

Embodiments 1 to 5 are particularly suitable for accurately obtainingthe high-density and high transfer-rate recording conditions.

Embodiment 6

In Embodiments 1 to 5, the optimum recording pulse waveform was obtainedby changing the recording pulse width and position. The presentembodiment involves a test write method in which, using the disc used inEmbodiment 2, the optimum recording waveform is obtained by changing therecording power while employing the same pulse start position for theeven-number length marks and odd-number length marks. Specifically, asshown in FIG. 12, ΔT shown in FIG. 2 was considered zero, and such Pw1and Pw2 were determined that the jitter could be minimized, where Pw 1is the recording power for the even-number length mark and Pw2 is therecording power for the odd-number length marks. As a result, theminimum jitter was obtained when Pw1 was 18.5 mW and Pw2 was 18.2 mW.

While in the present embodiment the recording power for the first pulsewas varied, the recording power of intermediate pulses or that of thelast pulse may also be varied. Although by individually setting therecording power for these pulses, the laser power level increases andthe recording waveform could be more complicated, there can be obtainedthe advantage that an optimum recording condition can be obtained.

While the power level is varied in the present embodiment, it is alsopossible to vary the pulse width simultaneously in addition to the powerlevel in order to determine optimum recording conditions, although thismay make the embodiment more complicated.

Embodiment 7

In the present embodiment, the start positions of the first pulse forthe even-number length mark and the odd-number length mark are alignedif certain conditions are satisfied in the 2T-based strategy.

In the present embodiment, the same disc as the one used in Embodiment 2was used, and the linear velocity was also the same as that inEmbodiment 2 at about 31.7 m/s. FIG. 13 shows a flowchart of theoperation of the test write method according to the present embodiment.In a first step (S401), the recommended recording power recorded on thedisc was read, obtaining a recording power (Pw) of 18 mW, an erasingpower (Pe) of 3.4 mW, and a bias power (Pb) of 0.25 mW. In a second step(S402), laser power conditions were set in these vicinities, and a testwrite was carried out on the disc in a third step (S403). The laserpower conditions were such that Pw was varied between 16 mW and 20 mW inincrements of 0.2 mW and Pe was varied between 3.1 mW and 3.7 mW inincrements of 0.2 mW, with the value of Pb fixed. As a result of thetest write in the third step (S403), a minimum jitter of 4.5% wasobtained when Pw was 18.2 mW and Pe was 3.2 mW in a fourth step (S404).These steps are identical to those of Embodiment 2.

Using the optimum recording power selected in the fourth step (S404), arecording was then carried out in order to determine the optimumconditions for the recording pulse width of the recording mark and therecording pulse start position. In the present embodiment, a randomsignal was used as the test-write recording pattern, as in Embodiment 3.The flow from S406 to S411 is substantially the same as that ofEmbodiment 3 and is therefore not described for simplicity. As a resultof the test write, an optimum ΔT (see FIG. 2) of 0.1T and an optimumjitter of 5.1% were obtained in an 11^(th) step (S411).

Then, in a 12^(th) step (S412), a substantially intermediate position T0between a first pulse start position T1 of an even-number length markand a first pulse start position T2 of an odd-number length mark. FIG. 7shows an example of the relationship between the first pulse startpositions T1 and T2, the intermediate position T0, and the jitter. Inthe present embodiment, the predetermined value of jitter was 5.8%.Jitter σ1 when the first pulse start position of the even-number lengthmark was T0 was measured (S413). Similarly, jitter σ2 when the firstpulse start position of the odd-number length mark was T0 was measured(S414). It was then determined in step 415 whether or not σ1 and σ2 aresmaller than the predetermined value. Since σ1 was 5.7% and σ2 was 5.3%in the present embodiment, which were below the predetermined value, thefirst pulse start position for the even-number length mark and theodd-number length mark was determined to be T0. By thus aligning thefirst pulse start position for the even-number length mark and theodd-number length mark, although the reproduction characteristics aresomewhat adversely affected, the recording waveform can be simplifiedand higher speeds can be achieved in an actual recording.

While in the present embodiment the first pulse start position was usedas the parameter for determining the intermediate point, the recordingpower may alternatively be used as the parameter as in Embodiment 6. Inthis case, an intermediate power (Pw1+Pw2)/2 between Pw1 and Pw2indicated in Embodiment 6 would be the set power.

Further, while jitter was used in the above embodiment as thecharacteristics evaluation means, a level jitter that is applied in PRMLmay alternatively be used.

Embodiment 8

The present embodiment involves an apparatus for carrying out the testwrite according to the above-described embodiments and an actualrecording. The apparatus is of a 2T-based strategy such as that ofEmbodiment 2, for example. The apparatus is generally shown in FIGS. 8and 14. Recording data is converted into recording code words in anencoding circuit and then composed with a synchronizing signal generatedin a synchronizing signal generating circuit. The composed signal isentered into a pulse conversion circuit where it is converted into pulsedata, which is further shaped into pulses in a recording pulse shapingcircuit for driving a light source. The processes up to this point areidentical in both FIGS. 8 and 14.

The even-number length marks and odd-number length marks are classifiedin order to produce a recording pattern. The apparatus shown in FIG. 8is equipped with an even/odd classified test-write pattern generatingcircuit. The even/odd classified test-write pattern generating circuitgenerates a test-write recording pattern consisting of even-numberlength marks and a test-write recording pattern consisting of odd-numberlength marks, and then records them on the disc. The signals recorded onthe disc are detected by a detection circuit, and the reproductionperformance is evaluated by a reproducing circuit. The next pulsewaveform is determined by a pulse waveform determining circuit, and thepath returns to the recoding pulse shaping circuit via an adjustmentamount memory means. In the pulse waveform determining circuit, pulseshapes such as the duty ratio of an intermediate pulse, the first pulsewidth, the last pulse width, the fall pulse width of a cooling levelafter the irradiation of the last pulse, individual recording powervalues, and the first pulse start position, for example, can be changed.While an even/odd classified test-write pattern generating circuit wasdescribed with reference to FIG. 8, any test-write pattern generatingcircuit may be used as long as it is capable of classifying the markswith lengths that are n times the window margin, where n is a naturalnumber, according to the remainder when n is divided by an integerconstant of 2 or more.

FIG. 14 shows an example of the apparatus in which a random signal isused instead of using individual test-write recording patterns foreven-number lengths and odd-number lengths. The random signal recordedin a test write is detected by a detection circuit and then classifiedinto even-number length marks and odd-number length marks in an even/oddclassifying circuit. The apparatus shown in FIG. 14 ischaracteristically equipped with a reproduction circuit, a pulsewaveform determining circuit, an adjustment amount memory circuit, and arecording pulse shaping circuit for the even-number length marks and theodd-number length marks individually. These circuits can be easilyrealized on a single circuit, and it is also easy to increase the numberof each circuit to more than one. While in the example of FIG. 14 aneven/odd classifying circuit was described, any classifying circuit maybe used as long as it is capable of classifying the marks with lengthsthat are n times the window margin, where n is a natural number,according to the remainder when n is divided by an integer constant of 2or more.

1. An information recording method for recording recording codes on aninformation recording medium using a predetermined write strategy, themethod comprising: recording a random signal on the informationrecording medium, the random signal consisting of a plurality ofrandomly arranged odd-number length marks and even-number length marks;classifying read signals of the random signal into read signalscorresponding to the odd-number length marks and read signalscorresponding to the even-number length marks; and independently settingposition conditions of recording pulses for the odd-number length marksand position conditions of recording pulses for the even-number lengthmarks that constitute the write strategy based on the classified readsignals.
 2. The information recording method according to claim 1,wherein position conditions of recording pulses used for recordingodd-number length marks among the recording pulses that constitute thewrite strategy are set using the read signals corresponding to theodd-number length marks, and position conditions of recording pulsesused for recording even-number length marks among the recording pulsesthat constitute the write strategy are set using the read signalscorresponding to the even-number length marks.
 3. The informationrecording method according to claim 2, further comprising: furtheradjusting the previously set start positions of irradiating first pulsesof the recording pulses used for recording the even-number length marksand the previously set start positions of irradiating first pulses ofthe recording pulses used for recording the odd-number length marks. 4.The information recording method according to claim 1, wherein annT-based write strategy is used as the write strategy, where n is anatural number and T is a reference clock period, the read signals ofthe random signal are classified according to mark lengths of marksrepresented by the product obtained by multiplying the remainder of then divided by an integer, which is not less than 2, and the T, andposition conditions of recording pulses used for recording marks withmark lengths, which are represented by the product of the remainder andthe T, are set based on the classified read signals.
 5. The informationrecording method according to claim 4, wherein a 3T-based write strategyor a 4T-based write strategy is used as the nT-based write strategy. 6.A trial write method for setting a recording condition for the recordingof recording codes on an information recording medium using apredetermined write strategy, the method comprising: recording a randomsignal on the information recording medium, the random signal consistingof plurality of randomly arranged odd-number length marks andeven-number length marks; classifying read signals of the random signalinto read signals corresponding to the odd-number length marks and readsignals corresponding to the even-number length marks; and independentlysetting position conditions of recording pulses for the odd-numberlength marks and position conditions of recording pulses for theeven-number length marks that constitute the write strategy based on theclassified read signals.